# Homework Help: Drop in Concentration as reaction progresses

1. Dec 9, 2007

### jaz1409

1. The problem statement, all variables and given/known data

I am currently doing an investigation into the reaction between different acids and magnesium metal. I want to try and show that by using a large volume of acid the concentration drop as the reaction progresses is significantly reduced. Is there any way of doing this?

2. Relevant equations

Mg (s) + 2 HCl (aq) --> H2 (g) + MgCl2 (aq)
Mg (s) + 2 H+ (aq) --> H2 (g) + Mg+2 (aq)

3. The attempt at a solution

Well I thought that by working out the moles of H+ ions present at the beginning of the reaction and at the end of the reaction may help. Other than that, I would just like to be pointed in the right direction.

2. Dec 10, 2007

### chemisttree

You could remove an aliquot of solution at several intervals and titrate the acid. Plot the concentration of acid vs time for your result.

The results might surprise you, though...

3. Dec 10, 2007

### jaz1409

well, so far I have found out the number of moles of HCL in 100cm3 of acid and then found the number of moles of H+ ions. I then found the percentage drop.

4. Dec 10, 2007

### chemisttree

What did you notice about the reaction rate?

5. Dec 11, 2007

### jaz1409

well, I worked out that the maximum drop in concentration theoretically was 5.20% which for a concentration of 0.8 M is not significant.

6. Dec 11, 2007

### chemisttree

Thats what I thought would happen. Also, the metal surface area is shrinking during the reaction. This will cause the greatest change in rate of reaction.